National Physical Laboratory

About: National Physical Laboratory is a facility organization based out in London, United Kingdom. It is known for research contribution in the topics: Dielectric & Thin film. The organization has 7615 authors who have published 13327 publications receiving 319381 citations.

A Radiometric Determination of the Stefan-Boltzmann Constant and Thermodynamic Temperatures between -40 degrees C and +100 degrees C

Abstract: The total radiant exitance of a black body at the temperature of the triple point of water, T$\_{\text{tp}}$ (273.16 K), and at a series of other temperatures in the range from about 233 K (-40 degrees C) to 373 K (100 degrees C), has been measured by using a cryogenic radiometer. From the measurements at T$\_{\text{tp}}$ a value for the Stefan-Boltzmann constant $\sigma $ has been calculated: $\sigma $ = (5.669 67 $\pm $ 0.000 76) $\times $ 10$^{-8}$ W m$^{-2}$ K$^{-4}$. This is the first radiometric determination of $\sigma $ having an uncertainty comparable with that calculated directly from fundamental physical constants. This measured value differs from the calculated one by 13 parts in 10$^{5}$, which is less than the combined standard deviations of the measured and calculated values. From the measurements of exitance at the other temperatures, values of the corresponding thermodynamic temperature T have been calculated by using Stefan's fourth-power law. Since the temperature of the radiating black body was also measured by platinum resistance thermometers calibrated on IPTS-68, values of (T-T$\_{68}$) were obtained. These range from about -(5 $\pm $ 1.6) mK at 20 degrees C to -(28 $\pm $ 2.5) mK at 100 degrees C and +(5 $\pm $ 1.5) mK at -40 degrees C. The results confirm to within a few millikelvins the departure of T$\_{68}$ from T above 0 degrees C already discovered by gas thermometry and show that similar departures, but of opposite sign, exist down to the lowest temperature measured, -40 degrees C. The uncertainties associated with these new values of T and (T-T$_{68}$) are similar to those of the best gas thermometry.

FTIR and circular dichroism spectroscopic study of interaction of 5-fluorouracil with DNA.

Abstract: 5-Fluorouracil (5FU) is an anticancer chemotherapeutic drug which exerts cytotoxic effect by inhibiting cellular DNA replication. In the present study, we explore the binding of 5FU with DNA and resulting structural and conformational changes on DNA duplex. UV-visible, Fourier transform infrared (FTIR) and circular dichroism (CD) spectroscopic techniques were employed to explore these interactions. A constant concentration of calf thymus DNA was incubated with varying concentrations of 5FU. UV-visible and FTIR spectroscopic results revealed that intercalation is the primary mode of interaction between 5FU and nitrogenous bases of the nucleic acid. The binding constant was found to be 9.7×10(4); which is indicative of moderate type of interaction between 5FU and DNA duplex. It was also observed that 5FU intercalates slightly more between AT base pairs compared to GC pairs. FTIR and circular dichroism spectroscopic results revealed that 5FU disturbs native B-conformation of DNA though, DNA remains in its B conformation even at higher concentrations of 5FU.

Critical Review of the Current Status of Thickness Measurements for Ultrathin SiO2 on Si, Part V: Results of a CCQM Pilot Study

Abstract: A study was carried out for the measurement of ultrathin SiO on (100) and (111) orientation silicon wafer in the thickness range 1.5-8 nm. XPS, medium-energy ion scattering spectrometry (MEIS), nuclear reaction analysis (NRA), RBS, elastic backscattering spectrometry (EBS), SIMS, ellipsometry, gazing-incidence x-ray reflectometry (GIXRR), neutron reflectometry and transmission electron microscopy (TEM) were used for the measurements. Water and carbonaceous contamination about 1 nm were observed by ellipsometry and adsorbed oxygen mainly from water at thickness of 0.5 nm were seen by MEIS, NRA, RBS and GIXRR. The different uncertainty of the techniques for the scaling constant were also discussed.